DESCRIPTION (provided applicant): Osteoporosis is characterized by reduced bone strength that results in an increased risk of fracture, in the US, 1-2 million men ages 50 years or older are affected by osteoporosis. The contribution of reduced bone density to osteoporosis and fracture risk is well known. However, attention has turned toward bone geometry as another skeletal feature that may influence fracture risk. Bone geometry is determined by the relative amounts of tissue on the inner and outer bone surfaces. From a biomechanical perspective, bone strength is vitally dependent on geometry. The characteristics among older men that influence bone geometry and bone strength are virtually unknown. Bone growth and resorption are regulated through biologic pathways that involve mechanical loading from muscle forces, as well as non-mechanical factors such as endocrine effects. Therefore, we hypothesize that bone geometry in the hip and spine among older men will be associated with abdominal body composition and with endogenous levels of testosterone and estradiol. Abdominal muscles may directly affect mechanical loads on the hip and spine. Abdominal adipose tissues may affect overall loading patterns or may exert endocrine influences on bone. In older men, testosterone appears to stimulate bone growth and estradioi may inhibit bone loss. To test the hypothesized associations, we propose to use existing data from 1,800 US men ages 65 years and older who are participants in the Osteoporotic Fractures in Men (MrOS) cohort. Quantitative computed tomography (QCT) scans have been performed in this cohort. Bone geometry measures in the hip and spine and abdominal body composition measures are derived from these scans. Assays for testosterone and estradiol have also been performed for these participants. We will quantify the associations of bone geometry in the hip and spine with abdominal body composition, testosterone and estradiol using a cross-sectional design. The proposed project will yield new information about factors that influence bone geometry among older men. [unreadable] [unreadable]